The Morphology and Evolution of Turbidity Channel System and Seabed Pockmarks: Case Study From the X Oilfield in Niger Delta Basin, West Africa

Abstract

Turbidity channel systems are a common type of sandstone deposit on the continental slope and have proven to be one of the most common types of reservoirs found in deep ocean settings. Channel-levee systems form coarse-grained sediment deposited along channel-axes and fine-grained sands deposited on levees, the morphology and evolution of channel-levee systems are of interest to the petroleum industry. This study focuses on two channel-levee system examples in the Niger Delta basin, West African. An example of deep-buried channel-levee system, and another example of pockmark and shallow-buried channel system in submarine were illustrated. The study area is located on the western Niger Delta slope between water depths of 1200 and 1500 m. It covers an area of about 1250 km² and supplied by the Niger River. The high-quality 3D seismic volume used in this study is with 12.5 m bin spacing, and dominant frequency is near 70 Hz (approximately 7 m vertical resolution). Several conclusions are obtained from this research: (1) The turbidity channel system is characterized by both meander loop expansion (swing) and meander loop down-system migration (sweep) as it evolved through time. Single channels of different periods inner channel complex show the feature of lateral and down-system migration, which has some succession. The later channel are influenced by earlier channel in morphology, curvature and width. The morphology of two adjacent channels are similar in channels' vertical evolution. (2) There is a consistent increase in sinuosity through time. Based on the similar morphology, the curvature of the later channel system increased and even cut-off in the high curvature site. In the curved segments, the later channel developed relatively a large axis migration and the curvature increased, and it is contrary in straight segments. (3) Seabed pockmarks are a widespread feature of the study area. Pockmarks and the shallow-buried channels were recognized in study area. The pockmarks are circular or elliptical in plan view. The distribution pattern of the pockmarks has a high consistency with the deposition form of the shallow-buried channel system. These depositional boundary-related pockmarks are formed by the fluids migrating along the channel boundary. Obviously, the formation and distribution of the pockmarks controlled by the shallow-buried channel system, we hypothesize that pockmark is a pre-requisite for creation of initial channels in deep-sea environments.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015